Dentin bonding procedures and dentin caries involve demineralization of the dentin structure. However, dentin is not homogeneous, and there are marked structure-property variations with various dentin types and locations. Such variations have important implications for long lasting bonds, and in order to improve restorative and preventive treatments it is necessary to clarify our understanding of demineralization phenomena. The overall hypothesis of this work is that in vitro dentin demineralization and shrinkage processes are dependent on specific structural variations of dentin. Preliminary atomic force microscopy (AFM) and x-ray tomographic microscopy (XTM) studies suggest a three layer model can be developed to understand dentin demineralization. The top layer is mineral free. Below this, is a second layer with a relatively uniform mineral content and this layer covers the deeper fully mineralized dentin. The dependence of these layers on specific demineralizing agents and concentration (aims 1 & 2), local dentin structure (aim 1) such as tubule number density, smear layer (aim 3) or coronal vs root dentin (aim 4), and alterations in the structure due to aging or disease processes (aim 5) will be clarified. We will also use the refined layer model to evaluate the effects of hydration, dehydration and shrinkage, and determine the effects of agents that could stabilize or fix the demineralized collagen scaffold, thus preventing its collapse during demineralization or drying (aim 2). Mineral density gradients in the subjacent layer will be determined and gradient variations with agent will be identified, aa well determination of any in this layer. Finally, key factors that significantly alter the parameters of the model will be evaluated for their impact on bonding interface integrity through evaluation of shear bond strength (aim 6). Such a critical evaluation of the model will lead to improved understanding of processes which significantly impact preventive and restorative dentistry.